Woodstoves are widely manufactured and commonly used for space heating in areas where wood is abundant and inexpensive, and other fuels may be not as readily available and more expensive.
The design of woodstoves has progressed to include separate controllers for primary and secondary combustion air. Primary air controllers are available which are either manually operable or thermostatically operable, to provide automatic regulation of primary air in response to room temperature, so as to maintain a relatively constant room temperature. Secondary air controllers are available which are manually adjustable to promote efficient combustion. Certain automatic secondary air controllers have also been developed, but generally require electrical power to operate electrical or electronic components. In remote areas, electrical power may not be readily available, or may be somewhat unreliable and subject to outages, particularly during storm conditions. It is very desirable to provide woodstoves which do not require any electrical power, so that the woodstoves will be fully usable as regular or emergency space heaters, even during electrical power outages, which often occur in bad weather, when the reliable availability of heat is acutely important.
Some woodstoves are provided with catalytic combustion plates for catalytically promoting the complete combustion of carbon monoxide (CO) and hydrocarbon gases and vapors emanating from the primary combustion zone in a woodstove. Typically, a catalytic combustion plate comprises a ceramic grid or honeycomb, coated with a combustion catalyst such as platinum, palladium, or a mixture thereof, for example. An adequate but well regulated supply of secondary air is particularly important for the best operation of a catalytic combustion plate, for achieving substantially complete catalytic combustion, without any need for unnecessarily heating excess secondary air. Consequently, the provision of an automatic secondary air controller is particularly advantageous in a woodstove having a catalytic combustion plate.